1. Field of the Invention
The present invention relates to a deflection yoke for a cathode ray tube, and in particular, to a deflection yoke having a correction unit to improve the assembly and productivity thereof, and to effectively control corrections during processing.
2. Description of Related Art
Generally, a cathode ray tube includes a neck with an electron gun mounted therein, a funnel with a deflection yoke mounted on the outer circumference thereof, and a panel with a shadow mask and a phosphor film. Electron beams emitted from the electron gun are deflected by a deflection magnetic field generated from the deflection yoke. The deflected electron beams pass through the shadow mask with a color selection function colliding against the phosphor film and emitting light to display desired images.
A horizontal deflection coil is mounted on the outer circumference of the funnel, and a vertical deflection coil is provided external to the horizontal deflection coil. A core (ferrite core) covers the vertical deflection coil. A horizontal deflection electric current is flowed through the horizontal deflection coil to generate a horizontal deflection magnetic field, and a vertical deflection electric current is flowed through the vertical deflection coil to generate a vertical deflection magnetic field.
The electron beams emitted from the electron gun directly proceed toward the phosphor film due to the attractive force of the positive electrode voltage, and enter into the region where the deflection magnetic field generated from the deflection yoke exists. Then, the electron beams are deflected due to the deflection electric current upon receipt of the force according to Fleming's left-hand rule from the deflection magnetic field, and are scanned on the phosphor screen, thereby displaying the desired images.
With the operation of uniform horizontal and vertical deflection magnetic fields, the area (space) in which the electron beams are passing through is roughly formed in a shape of a pyramid. The apex of the pyramid corresponds to the deflection center of the deflection yoke, and a geometric distortion GD called a pincushion is made at the cross point of the surface of the screen with a large curvature radius and the pyramid. The horizontal deflection magnetic field generated due to the horizontal deflection coil causes formation of a pincushion type of magnetic field, and the vertical deflection magnetic field generated due to the vertical deflection coil causes formation of a barrel type of magnetic field. In this regard, a north-south (NS) pincushion distortion and an east-west (EW) pincushion distortion are caused due to those deflection magnetic fields.
The geometric distortion GD is also caused by the difference in the left and right magnetic fields due to the relative distribution of the left and right vertical deflection coils and the dimension of the relative amount of current.
Particularly with the conventional cathode ray tube, as the screen is increased in size and flattened, the distortion from the deflection point increases toward the periphery of the screen. When the electron beams are deflected, the deflection at the farthest four corners is increased so that the NS pincushion distortion is mainly caused in the north-south direction of the screen. Furthermore, as the screen is increased in size, flattened, and made to have a higher definition, a raster distortion, an east-west (EW) pincushion distortion, and an inner distortion are produced.
When the geometric distortion GD is produced in various manners, the picture on the screen becomes twisted.
In order to correct the geometric distortions, a GD correction unit is conventionally mounted in the case or chassis of a TV set or a monitor set.
However, when the GD correction unit is mounted in the case or chassis, it is spaced apart from the location of the deflection yoke (the outer circumference of the funnel), and hence, the desired correction effect is not obtained satisfactorily.
Furthermore, in the manufacturing process, it is impossible to control the amount of correction of the GD correction unit before assembling the case or chassis. Accordingly, if the units are defective, the resulting loss is substantial. Therefore, the correction should be made before the completion of assembly to reduce the resulting loss.